diff --git a/ChangeLog b/ChangeLog
index d4d739d21b..24c8696c55 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Tue Mar 29 21:51:31 2011  CHIKANAGA Tomoyuki  <nagachika00@gmail.com>
+
+	* string.c (rb_String): Kernel#String should call to_str before to_s.
+
 Tue Mar 29 10:28:08 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* test/webrick/test_filehandler.rb
diff --git a/object.c b/object.c
index b25c0af1c2..fad726cd73 100644
--- a/object.c
+++ b/object.c
@@ -2360,7 +2360,10 @@ rb_num2dbl(VALUE val)
 VALUE
 rb_String(VALUE val)
 {
-    return rb_convert_type(val, T_STRING, "String", "to_s");
+    VALUE tmp = rb_check_string_type(val);
+    if (NIL_P(tmp))
+	tmp = rb_convert_type(val, T_STRING, "String", "to_s");
+    return tmp;
 }